The present invention relates to a sealing material for producing liquid crystal display panels, and more particularly to a sealing material for producing liquid crystal display panels of which the base plates are made of flexible polymer film.
Conventional liquid crystal display apparatuses which are now in general use comprise a rigid case made of a metal or hard synthetic resin, and a liquid display panel of which base plates are made of inorganic glass and are fitted into the rigid case, with a liquid crystal being sealed between the base plates. These conventional liquid crystal display apparatuses have several shortcomings. For example, they are heavy and fragile, since the base plates are made of inorganic glass which is itself heavy and fragile. Due to the use of these fragile inorganic glass base plates, care must be taken when handling or carrying the display apparatus. It is also difficult to work the base plates into the desired shapes. In order to protect the display panel, a very rigid and strong case is indispensable. The result is that they are heavy and not suitable in many applications.
In order to eliminate these shortcomings of the conventional liquid crystal display apparatuses, there has been proposed the replacement of the inorganic-glass-made base plate by a polymer film which is flexible, light but strong, and excellent in workability. However, when constructing such a liquid crystal display panel in which a liquid crystal is sealed between base plates made of such a polymer film, the conventional adhesive agents, for instance, epoxy adhesive agents that are used for sealing the inorganic glass base plates, do not provide sufficient sealing with the polymer film.
Before explaining the necessary conditions for a sealing material for use in such polymer-film-made liquid crystal display panel, the structure of an example of a liquid crystal display panel, which is described in Japanese patent application No. 56-152274 filed on Sept. 24, 1981, will now be explained by referring to FIG. 1, which schematically shows the cross section of a liquid crystal display panel.
In the figure, reference numeral 1 represents an upper base plate; reference numeral 2, a lower base plate; reference numerals 3 and 4 each, transparent electrodes; reference numeral 5, a lead electrode; reference numeral 6, a thin film; reference numeral 7, an upper and lower liquid-crystal-orientation processed film; reference numeral 8, spacer particles for maintaining the gap between the upper and lower liquid-crystal-orientation processed films 7; reference numeral 9, a twisted-nematic liquid crystal (hereinafter simply referred to as the liquid crystal); reference numeral 10, a polarizer; and reference numeral 11, a sealing material.
As can be seen from the figure, in the constructed state, the sealing material 11 is in contact with the liquid crystal 9, the orientation-processed film 7, the transparent electrodes 3 and 4, the lead electrode 5, the upper base plate 1 and the lower base plate 2. Further, in the course of producing such liquid crystal display panels, the sealing material 11, before it becomes hard, may come into contact with, for example, the liquid crystal 9, the orientation processed film 7, the transparent electrode 3 and the base plates 1 and 2. Because of this possibility, common sealing materials containing solvents have the following shortcomings, if they are used for the liquid crystal display panels of the above-mentioned type:
1. The adhesion strength between the polymer film and the other elements is not high enough and cannot be maintained uniform over a long period of time.
2. The sealing material has adverse effects, for instance, causes deterioration of the liquid crystal, the orientation processed films, the transparent electrodes, the base plates or other elements with which the sealing material may come into contact, before and after the sealing material becomes hard.
3. If the sealing material is not of a solvent-free type, the above-mentioned adverse effects are considerable.
4. If the sealing material does not retain its flexibility after it becomes hard, a key feature of the liquid crystal display panel employing base plates made of polymer film, i.e., that the liquid crystal display panel is flexible, is not attained.
For such a particular use, sealing materials which can meet the above-described conditions have not been proposed, and, therefore, a liquid crystal display panel made of such a polymer-film has not been produced for practical use. This is inspite of the fact that a great number of sealing materials and adhesive agents have been produced and put on the market for general use or for other purposes.